Macrocellular acoustic foam containing particulate additive

ABSTRACT

A cellular thermoplastic polyolefin foam comprising at least one particulate additive in admixture with a polymer matrix is disclosed, along with a process and foamable gel for manufacturing the same, wherein the polyolefin matrix comprises at least one polymer resin graft-modified with at least one polar group selected from the group consisting of acid, acid ester, and acid anhydride, and salts thereof. The invention facilitates the manufacture of macrocellular foams useful for acoustic absorption having increased amounts of particulate additives that provide certain desired properties difficult to achieve without the particulate additives, such as improved flame retardancy.

CROSS REFERENCE STATEMENT

This application claims the benefit of U.S. Provisional Application No.60/358,832, filed Feb. 22, 2002.

BACKGROUND OF THE INVENTION

Foams and foamed articles often find utility in acoustic systems forsound absorption and insulation. Such foams, when developed fordifferent market segments (appliance, automotive, industrial, buildingand construction, etc) often need to meet certain acoustic performancerequirements and there is also a desire to add certain particulateadditives to foams to obtain certain desired properties. An example ofsuch particulate additives are fire retardants and fire retardantadjuvants to meet certain fire-test-response characteristics (ASTME176).

Unfortunately, the typical particulate additives, when added to thepolymer resin formulation, often cause a number of problems during themanufacture of the foam that have an adverse affect on obtainingacoustically active macrocellular foams. They often act as nucleatingagents in the foaming process and provide additional nucleation sites,resulting in the formation of a large number of small cells withvariable properties. Unfortunately, foams having an average cell sizeless than 1.5 millimeter (mm) are often not as desirable as foams havinga larger average cell size in certain end use applications, such asacoustic absorption.

U.S. Pat. No. 4,277,569 teaches the preparation of flame retardantpolyolefin foams for thermal insulation and padding. However, thatpatent does not describe macrocellular foams or flame retardantmacrocellular foams for acoustic applications or their preparation.

Japanese Laid Open Patent Application No. 10-204200 describes olefinresin foams for use in vacuum molding made from 100 parts by weight ofan olefin type resin comprising 30 to 90 percent by weight propylenetype resin and 70 to 10 percent by weight ethylene type resin, 1 to 100parts by weight of a brominated compound and 0.1 to 10 parts by weightof antimony trioxide having an average particle size of 0.4 microns orsmaller. Macrocellular foams useful for acoustic applications are notdescribed.

WO 00/15697 describes a macrocellular acoustically active foam which maybe surface treated with a solution containing certain fire retardantmaterials. While that procedure is able to confer fire retardancy, itrequires the extra steps of treating the foam after extrusion andperforation and then drying the foam to remove the liquid media used toapply the fire retardant.

Therefore, a significant market need still exists for a large cell,acoustically active foam containing particulate additives. This need isnot only generally applicable to polymer foams, but is also particularlyacute in the area of thermoplastic foams (that is, foams that aresubstantially uncrosslinked and capable of being remelted) and foamsthat also resist water absorption such that they may be used in humid orwet environments without losing performance or potentiating corrosion ormicrobial growth problems. These, and other problems as described below,are solved by the present invention.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention is a cellular polymer foamcomprising:

-   A) at least one particulate additive in admixture with-   B) a polymer matrix,    wherein the polymer matrix comprises at least one polymer resin    graft-modified with at least one polar group selected from the group    consisting of acid, acid ester, or acid anhydride, or salt thereof.

Another aspect of this invention is foamable gel for making the foamaccording to claim 1 comprising:

-   1) at least one particulate additive in admixture with at least one    polymer matrix and-   2) at least one blowing agent,    wherein the polymer matrix comprises at least one polymer resin    graft-modified with at least one polar group selected from the group    consisting of acid, acid ester, or acid anhydride, or salt thereof.

Yet another aspect of this invention is a method for making amacrocellular polymer foams containing at least one particulate additivecomprising expanding the aforementioned foamable gel.

Yet another aspect of this invention is the use of the abovemacrocellular acoustic foam as an acoustic absorption or acousticinsulation material.

This invention is further described in the detailed description whichfollows.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

All references herein to elements or metals belonging to a certain Grouprefer to the Periodic Table of the Elements published and copyrighted byCRC Press, Inc., 1989. Also any reference to the Group or Groups shallbe to the Group or Groups as reflected in this Periodic Table of theElements using the IUPAC system for numbering groups.

Any numerical values recited herein include all values from the lowervalue to the upper value in increments of one unit provided that thereis a separation of at least 2 units between any lower value and anyhigher value. As an example, if it is stated that the amount of acomponent or a value of a process variable such as, for example,temperature, pressure, time and the like is, for example, from 1 to 90,preferably from 20 to 80, more preferably from 30 to 70, it is intendedthat values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. areexpressly enumerated in this specification. For values which are lessthan one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 asappropriate. These are only examples of what is specifically intendedand all possible combinations of numerical values between the lowestvalue and the highest value enumerated are to be considered to beexpressly stated in this application in a similar manner. In particular,the end points of ranges for a particular subject are intended to befreely combinable with other stated ranges for the same subject unlessstated otherwise, for example, a stated lower end of a range may becombined with a stated upper end of a range for the same subject, suchas average cell size.

The term “micron” means one-millionth of a meter and is interchangeablewith the term “micrometer” and the abbreviation “μ”.

Unless stated otherwise, the term “flame retardant” when used by itselfmeans any compound or mixture of compounds which imparts flameresistance to the foam compositions of the present invention other thanthe particulate flame retardant adjuvants described below. This termincludes, but is not limited to, organic flame retardants such ashalogen-containing compounds or mixtures of compounds.

The term “particulate additive” means an additive that is in the form ofdetectable discrete particles in the polymer matrix of the foams of thisinvention not only at room temperature, but also at the temperature ofthe polymer(s) comprising the polymer matrix during expansion of thefoam. That temperature is generally the lowest temperature at which allthe polymer components of the polymer matrix are in a molten statehaving a viscosity appropriate for foam expansion. Alternatively or inaddition, the term may be defined to include any additive that, whenadded to a foamable gel at a conventional rate, or if there is noconventional rate then at 5 phr, results in a measurable decrease in theaverage cell size of the foam made from the foamable gel compared to afoam made under the same conditions except that the foamable gel doesnot contain the particulate additive.

The term “particulate flame retardant adjuvant” means particulatematerials which increase the flame resistance of the foam compositionsof the present invention when they are present in an amount of at least1 part per hundred parts of total polymer resin (phr). Preferably theyenhance the effectiveness of flame-retardants that are also present inthe polymer matrix of the foam, including those in a form other than asparticles, such as most organic flame retardants. This term is intendedto include, but not be limited to, particulate flame retardantsynergists, char forming materials, smoke suppressants and particulateflame retardants. They are preferably primarily comprised of aninorganic compound or a mixture of inorganic compounds. Unless otherwisespecified herein, the term “flame retardant adjuvant” when used in thecontext of the present invention means “particulate flame retardantadjuvant” and the terms “flame retardant synergist” and “synergist” whenused in the context of the present invention means “particulate flameretardant synergist”. The flame retardant synergists are encompassed bythe more generic term “particulate flame retardant adjuvant”. The latterapplies by analogy to the particulate char forming materials and smokesuppressants, but the distinction in wording is maintained hereinbetween the generic expression “flame retardant” (without the term“adjuvant”) and the subgeneric expression “particulate flame retardant”.

The term “flame retardant package” means a combination of flameretardant(s) and flame retardant adjuvant(s) with each other. Acombination of flame retardant(s), flame retardant synergist(s) and,optionally, smoke suppressant(s) is a generic example of a fireretardant package.

The term “interpolymer” is used herein to indicate a polymer wherein atleast two different monomers are polymerized to make the interpolymer.This includes copolymers, terpolymers, etc.

The term “melt flow rate” as used herein means a flow rate measuredaccording to ASTM D1238, typically at 2.16 kg. When in reference toethylene polymers measured under the conditions of 2.16 kg, and 190degrees Celsius, the melt flow rate is generally referred to by the term“melt index”. For the sake of simplicity, the term “melt flow rate”shall be assumed to also include, unless stated otherwise, the meltindex values for ethylene polymers.

The term “macrocellular acoustic foam” is used herein to indicate a foamhaving an average cell size according to ASTM D3575 greater than 1.5 mm,more preferably at least 2 mm, even more preferably at least 3 mm, evenmore preferably at least 4 mm, and even more preferably at least 4.5 mm,preferably up to 20 mm, also preferably up to 15 mm, and for some enduses up to 10 mm is particularly preferred. At a thickness of 35 mm,macrocellular foams may have an average sound absorption coefficient(measured via ASTM E1050 at 250, 500, 1000 and 2000 hertz (Hz) soundfrequencies) of greater than 0.15, preferably greater than 0.20, morepreferably greater than 0.25, even more preferably greater than 0.30.

A) Particulate Additive

The particulate additive is an additive that is comprised of particleshaving an average particle size preferably not greater than 100 microns,more preferably not greater than 10 microns and still more preferablynot greater than 1 micron and preferably at least 0.01 micron, morepreferably at least 0.1 micron, and even more preferably at least 1micron. Preferably at least 65 percent of the particles have a particlesize within 50 percent, more preferably within 20 percent, of theaverage particle size of the particles per 100 g sample of the foam.

Unless specified otherwise, the average particle size referred to hereinis the volumetric average particle size. The average particle size andthe particle size distribution of the particulate additive as such maybe measured by appropriate conventional particle size measuringtechniques such as sedimentation, photon correlation spectroscopy, fieldflow fractionation, disk centrifugation, transmission electronspectroscopy, and dynamic light scattering. A preferred technique is tomeasure dynamic light scattering using a device such as a Horiba LA-900Laser Scattering particle size analyzer (Horiba Instruments, Irvine,Calif., USA). The volumetric distribution relates to the weightdistribution.

When the particulate additive is in the foam polymer matrix, the averageparticle size and particle size distribution may be determined usingtechniques known in the art. One approach is to use an electronmicroprobe, such as a Cameca SX-50 electron microprobe, to collectelement maps of the particles from a cross-section of the foam and thenuse a scanning electron microscope, such as a JEOL 6320 field emissionscanning electron microscope, to create an image of the mapped particlesto examine their surface and cross-sectional features. By overlaying theelemental map over the information derived from the scanning electronmicroscope image, one can selectively determine the average particlesize and particle size distribution of the particulate additive inquestion.

The particles are preferably substantially inorganic, that is, theypreferably have a surface that is predominantly non-hydrocarbon.Examples of inorganic particles include oxides, halides, borates,silicates and stannates of various elements selected from the PeriodicTable of Elements, particularly of metals, such as the transitionmetals, such as antimony, zinc, or tin, and metals selected from Group Ior Group II, such as magnesium, of the Periodic Table of Elements. Theparticles are preferably substantially solid at foam extrusiontemperatures.

Examples of suitable particulate additives are found among various flameretardant adjuvants, flame retardants, antioxidants such as phosphites(for example, Irgafos™ 168, which is a trademark of and available fromthe Ciba Geigy Corporation), antiblock additives, colorants, pigments,fillers, and acid scavengers.

Examples of particulate inorganic flame retardant adjuvants are foundamong particulate flame retardant synergists, char forming materials,and smoke suppressants.

Flame retardant synergists include, but are not limited to, metal oxidessuch as antimony trioxide, antimony pentoxide, iron oxide, tin oxide,zinc oxide, aluminum trioxide, alumina (for example, alumina having anaverage particle size less than 0.5 microns are available from NyacolNano Technologies, Inc.), bismuth oxide, molybdenum trioxide (forexample, molybdenum trioxide having an average particle size less than0.5 microns are available from Nyacol Nano Technologies, Inc.), andtungsten trioxide; zinc borate; antimony silicates; zinc stannate; zinchydroxystannate; ferrocene and mixtures thereof, antimony trioxide andantimony pentoxide being preferred. Antimony trioxide is available fromthe Great Lakes Chemical Corporation under the trademarks TRUTINT™ foraverage particle sizes of at least 1 micron and MICROFINE™ for averageparticle sizes less than 1 micron. Antimony pentoxide having an averageparticle size less than 0.1 micron is available under the trademarkNYACOL™ from Nyacol Nano Technologies, Inc. Ashland, Mass., U.S.A.

Particulate char forming materials include, but are not limited to, clayfillers, such as organoclay nanocomposites. Organoclay nanocompositeshaving an effective particle size less than 1 micron after incorporationinto the polymer matrix of a polymer foam of the present invention areavailable under the trademark CLOISITE™ from Southern Clay Products,Inc., Gonzales, Tex., U.S.A.

Particulate smoke suppressants include, but are not limited to, zincborate, tin oxide, and ferric oxide. Zinc borate having an averageparticle size less than 0.5 microns is available from Nyacol NanoTechnologies, Inc.

Solid particulate flame retardants include inorganic fire retardants,such as magnesium hydroxide and magnesium carbonate. Magnesiumhydroxide, preferably having a particle size in the range from less than1 micron to at least 2 nanometers, is available from Nyacol NanoTechnologies, Inc., and is available from Morton InternationalCorporation under VERSAMAG™, such as VERSAMAG™ UF. Magnesium carbonateis also available from Morton International Corporation underELASTOCARB™, such as ELASTOCARB™ Tech Light and ELASTOCARB™ Tech High.

The flame retardants and flame retardant adjuvants may be usedindividually or in combination with each other. They, and other flameretardant adjuvants having the required and preferred particle sizes,may be made using techniques well known in the art, and may beincorporated into the polymer matrix. See, for example, U.S. Pat. No.5,409,980 incorporated herein by reference, which describes synergistsand combinations of the same with flame retardants suitable for thepresent invention.

Preferred examples of fillers are talc, carbon black, carbon fibers,calcium carbonate, alumina trihydrate, glass fibers, marble dust, cementdust, clay, feldspar, silica or glass, fumed silica, alumina, magnesiumoxide, magnesium hydroxide, antimony oxide, zinc oxide, barium sulfate,aluminum silicate, calcium silicate, titanium dioxide, titanates, glassmicrospheres or chalk.

Acid scavengers include, but are not limited to, zeolite andhydrotalcite.

Other particulate additives include calcium carbonate, talc, titaniumoxide, silica, barium sulfate, diatomaceous earth, mixtures of citricacid and sodium bicarbonate, and residual catalyst particles in thepolymer foam matrix that originate from a process used to make one ormore of the polymers in the polymer foam matrix, such as the processused to make LLDPE. The particulate additive may, for example, be anucleating agent, such as calcium carbonate, talc, clay, titanium oxide,silica, barium sulfate, diatomaceous earth, and the like.

The particles may be treated to reduce agglomeration or improvedispersibility in a polymer matrix or in certain media. Particulateantimony compounds may, for example, be surface modified with a couplingagent, such as with an organic titanate as described, for example, inU.S. Pat. No. 4,100,076. Antimony oxide particles, such as colloidalantimony pentoxide, may be treated to reduce degradation of the polymerresin while the resin is at an elevated temperature, such as duringextrusion of the foam of this invention, as taught in, for instance,U.S. Pat. No. 4,741,865. WO 00/64966 describes how to make certainvacuum de-aerated powdered polymer additives having a particle sizerange overlapping the less than one micron range, including flameretardant adjuvants suitable for use in the foams of this invention.Each of the above patents and published patent applications areincorporated herein by reference for their relevant disclosure.

The total amount of particulate additive is preferably at least 0.1 phr,more preferably at least 1 phr, and more preferably at least 2 phr, andpreferably up to 10 phr, more preferably up to 6 phr. The parts byweight per hundred parts by weight of resin (“phr”) are based on thetotal parts by weight of polymer in the polymer matrix of the foam.

B) Polymer Matrix

The polymers comprising the polymer matrix of the foam according to thepresent invention, and also used to make the foam and foamable gelstarting material according to the present invention, may be anypolymers capable of forming a foam structure. Preferred polymers arethermoplastic. They are preferably polyolefins, such as homopolymers andinterpolymers of α-olefin, vinyl aromatic monomer units, and/orfunctional monomers, and combinations thereof, and combinations (thatis, blends) of such polymers, as further described below.

Preferably the resin to be foamed comprises an ethylene or C₃-C₂₀α-olefin homopolymer resin, an ethylene/C₃-C₂₀ α-olefin interpolymer(including polyolefin elastomers, polyolefin plastomers, and/or one ormore substantially random interpolymers), or a blend of one or more ofthese polymers. The resin to be foamed may also comprise a blend of oneor more of said ethylene or C₃-C₂₀ α-olefin homopolymers with a secondpolymer component. This second polymer component can include, but is notlimited to, any of the above-mentioned polymers and is preferablyselected from ethylene/C₃-C₂₀ α-olefin interpolymers (includingpolyolefin elastomers, polyolefin plastomers, and/or one or moresubstantially random interpolymers), or combinations thereof.

In a preferred embodiment, the resin may also comprise a minor amount(that is, less than 50 weight-percent) of interpolymers of α-olefin withvinyl aromatic monomer units and/or functional monomers, which isblended with one or more of the α-olefin polymers. Preferred functionalmonomers include vinyl acetate, an alkyl acrylate such as methylacrylate or ethyl acrylate, and acrylic acid.

The α-olefin polymers are polymers or interpolymers containing repeatedunits derived by polymerizing an α-olefin. As defined herein, theα-olefin polymer contains essentially no polymerized monovinylidenearomatic monomers and no sterically hindered aliphatic or cycloaliphaticvinyl or vinylidene monomers. Particularly suitable α-olefins have from2 to about 20 carbon atoms, preferably from 2 to about 8 carbon atoms,and include ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene,1-octene and the like. Preferred α-olefin polymers are homopolymers ofethylene or propylene and interpolymers of ethylene with a C₃-C₈α-olefin. The α-olefin polymer may also contain, in polymerized form,one or more other non-aromatic monomers that are interpolymerizable withthe α-olefin and which contain an aliphatic or cycloaliphatic group.Such monomers include, for example, vinyl acetate, acrylic acid,methacrylic acid, esters of acrylic or methacrylic acid and acidanhydrides such as maleic anhydride. The α-olefin polymer preferablycontains at least 75 percent by weight, preferably at least 95 percentby weight, of polymerized α-olefin monomers. More preferably, theα-olefin polymer contains at least 85 percent by weight polymerizedethylene, with polymerized α-olefin monomers constituting the remainderof the polymer. In other words, the α-olefin polymer may containpolyethylene or a copolymer of ethylene and up to about 15 percent ofanother α-olefin.

Particularly suitable α-olefin polymers include low density polyethylene(LDPE), which term is used herein to designate polyethylene homopolymersmade in a high pressure, free radical polymerization process. These LDPEpolymers are characterized by having a high degree of long chainbranching. LDPE useful in this invention preferably has a density ofabout 0.910 to 0.970 g/cc, more preferably less than or equal to 0.935g/cc (ASTM D792) and preferably has a melt index of at least 0.02, morepreferably at least 0.05, even more preferably at least 0.1, and evenmore preferably at least 0.2, preferably up to 100, more preferably upto 50, even more preferably up to 30, and even more preferably up to 20,grams per 10 minutes (as determined by ASTM Test Method D1283, condition190° C./2.16 kg).

The so-called linear low density polyethylene (LLDPE) and high densitypolyethylene (HDPE) products are also useful herein. These polymers arehomopolymers of polyethylene or copolymers thereof with one or morehigher α-olefins and characterized by the near or total absence (lessthan 0.01/1000 carbon atoms) of long chain branching. LLDPE and HDPE aremade in a low pressure process employing conventional Ziegler-Natta typecatalysts, as described in U.S. Pat. No. 4,076,698, which isincorporated herein by reference. LLDPE and HDPE are generallydistinguished by the level of α-olefin comonomer that is used in theirproduction, with LLDPE containing higher levels of comonomer andaccordingly lower density. Suitable LLDPE polymers having a density offrom about 0.85 to about 0.940 g/cc (ASTM D792) and a melt index (ASTMD1238, condition 190° C./2.16 kg) of about 0.01 to about 100 grams/10minutes. Suitable HDPE polymers have a similar melt index, but have adensity of greater than about 0.940 g/cc.

LLDPE polymers having a homogeneous distribution of the comonomer aredescribed, for example, in U.S. Pat. No. 3,645,992 to Elston and U.S.Pat. Nos. 5,026,798 and 5,055,438 to Canich, which are incorporatedherein by reference.

Yet another type of α-olefin polymer are substantially linear olefinpolymers as described in U.S. Pat. Nos. 5,272,236 and 5,278,272,incorporated herein by reference. The substantially linear olefinpolymers are advantageously homopolymers of a C₂-C₂₀ α-olefin or,preferably, interpolymers of ethylene with at least one C₃-C₂₀ α-olefinand/or a C₄-C₁₈ diolefin. These polymers contain a small amount oflong-chain branching (that is about 0.01 to 3, preferably 0.01-1 andmore preferably 0.3-1 long chain branch per 1000 carbon atoms) andtypically exhibit only a single melting peak by differential scanningcalorimetry. Particularly suitable substantially linear olefin polymershave a melt index (ASTM D1238, Condition 190° C./2.16 kg) of from about0.01 to about 1000 g/10 min, and a density of from 0.85 to 0.97 g/cc,preferably 0.85 to 0.95 g/cc and especially 0.85 to 0.92 g/cc. Examplesinclude polyolefin plastomers, such as those marketed by The DowChemical Company under the trademark AFFINITY™ and polyethyleneelastomers, such as those marketed by Du Pont Dow Elastomers LLC underthe trademark ENGAGE™.

Another suitable α-olefin polymer includes propylene polymers. The term“propylene polymer” as used herein means a polymer in which at least 50weight percent of its monomeric units are derived directly frompropylene. Suitable ethylenically unsaturated monomers other thanpropylene that may be included in the propylene polymer, includeα-olefins, vinylacetate, methylacrylate, ethylacrylate, methylmethacrylate, acrylic acid, itaconic acid, maleic acid, and maleicanhydride. Appropriate propylene interpolymers include random, block,and grafted copolymers or interpolymers of propylene and an olefinselected from the group consisting of ethylene, C₄-C₁₀ 1-olefins, andC₄-C₁₀ dienes. Propylene interpolymers also include random terpolymersof propylene and 1-olefins selected from the group consisting ofethylene and C₄-C₈ 1-olefins. The C₄-C₁₀ 1-olefins include the linearand branched C₄-C₁₀ 1-olefins such as, for example, 1-butene,isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene,3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, and the like.Examples of C₄-C₁₀ dienes include 1,3-butadiene, 1,4-pentadiene,isoprene, 1,5-hexadiene, and 2,3-dimethyl-1,3-hexadiene. As used herein,the term “interpolymers” means polymers derived from the reaction of twoof more different monomers and includes, for example, copolymers andterpolymers.

The propylene polymer material may be comprised solely of one or morepropylene homopolymers, one or more propylene copolymers, and blends ofone or more of each of propylene homopolymers and copolymers. Thepolypropylene preferably comprises at least 70, even more preferably atleast 90, and even more preferably 100, weight percent propylene monomerderived units (that is, the propylene homopolymers are preferred).

The propylene polymer preferably has a weight average molecular weight(M_(w)) of at least 100,000. M_(w) can be measured by known procedures.

The propylene polymer also preferably has a branching index less than 1.The branching index is an approach to quantifying the degree of longchain branching selected for this particular invention. The definitionof branching index and procedure for determining the same is describedin column 3, line 65 to column 4, line 30, of U.S. Pat. No. 4,916,198,which is incorporated herein by reference. The branching index is morepreferably less than 0.9, and even more preferably less than 0.4.

The propylene polymer preferably has a tan δ value not greater than 1.5,preferably not greater than 1.2, even more preferably not greater than1.0, and even more preferably not greater than 0.8. Tan δ may becalculated from g″/g′, where g″ is the loss modulus of the propylenepolymer and g′ is storage modulus of the propylene polymer melt using a2.5 mm thick and 25 mm diameter specimen of the propylene polymer at 190C at a one Radian per second oscillating frequency. These parameters maybe measured using a mechanical spectrometer, such as a Rheometrics ModelRMS-800 available from Rheometrics, Inc., Piscataway, N.J., U.S.A.Further details of how to carry out this determination of the tan δ, g′and g″ values is provided in column 5, lines 59 to 64, and column 6,lines 4 to 29, of U.S. Pat. No. 5,527,573, which is incorporated hereinby reference.

In addition or in the alternative, the propylene polymer preferably hasa melt tension of at least 7 centiNewtons (cN), more preferably at least10 cN, and even more preferably at least 15 cN, and even more preferablyat least 20 cN. Preferably, the propylene polymer has a melt tension notgreater than 60 cN, more preferably not greater than 40 cN. The term“melt tension” as used throughout this description refers to ameasurement of the tension in cN of a strand of molten polymer materialat extruded from a capillary die with a diameter of 2.1 mm and a lengthof 40 mm at 230° C. at an extrusion speed of 20 mm/minute (min.) and aconstant take-up speed of 3.14 meter/minute using an apparatus known asa Melt Tension Tester Model 2 available from Toyo Seikl Seisaku-sho,Ltd. This method for determining melt tension is sometimes referred toas the “Chisso method”.

In addition or in the alternative, the propylene polymer preferably hasa melt strength of at least 10 centiNewtons (cN), more preferably atleast 20 cN, and even more preferably at least 25 cN, and even morepreferably at least 30 cN. Preferably, the propylene polymer has a meltstrength not greater than 60 cN, more preferably not greater than 55 cN.The term “melt strength” throughout this description refers to ameasurement of the tension in cN of a strand of molten polymer materialextruded from a capillary die with an diameter of 2.1 mm and a length of41.9 mm at 190° C. at a rate of 0.030 cc/sec. and stretched at aconstant acceleration to determine the limiting draw force, or strengthat break, using an apparatus known as a Gottfert Rheotens™ melt tensionapparatus available from Gottfert, Inc.

The propylene polymer used in the process of the invention preferablyalso has a melt elongation of at least 100 percent, more preferably atleast 150 percent, most preferably at least 200 percent as measured bythe same Rheotens™ melt tension apparatus and general proceduredescribed above.

The propylene polymer material preferably also has a melt flow rate ofat least 0.01 more preferably at least 0.05, even more preferably atleast 0.1 g/10 min., and even more preferably at least 0.5 g/10 min. upto 100, more preferably up to 50, even more preferably up to 20, andeven more preferably up to 10, g/10 min. Throughout this description,the term “melt flow rate” refers to a measurement conducted according toAmerican Society for Testing and Materials (ASTM) D1238 condition 230°C./2.16 kg. (aka Condition L).

In addition, α-olefin polymers that have been subjected to coupling orlight crosslinking treatments are useful herein, provided that theyremain melt processable. Such grafting or light crosslinking techniquesinclude silane grafting as described in U.S. Pat. No. 4,714,716 to Park;peroxide coupling as described in U.S. Pat. No. 4,578,431 to Shaw etal., and irradiation as described in U.S. Pat. No. 5,736,618 to Poloso,each of which is incorporated herein by reference. Preferably, thetreated polymer has a gel content of less than 10%, more preferably lessthan 5%, most preferably less than 2% by weight, as determined by gelpermeation chromatography. Treatment of this type is of particularinterest for HDPE, LLDPE or substantially linear polyethylenecopolymers, as it tends to increase the melt tension and melt viscosityof those polymers to a range that improves their ability to be processedinto foam in an extrusion process.

Preferred propylene polymers include those that are branched or lightlycross-linked. Branching (or light cross-linking) may be obtained bythose methods generally known in the art, such as chemical orirradiation branching/light cross-linking. One such resin which isprepared as a branched/lightly cross-linked polypropylene resin prior tousing the polypropylene resin to prepare a finished polypropylene resinproduct and the method of preparing such a polypropylene resin isdescribed in U.S. Pat. No. 4,916,198, which is hereby incorporated byreference. Another method to prepare branched/lightly cross-linkedpolypropylene resin is to introduce chemical compounds into theextruder, along with a polypropylene resin and allow thebranching/lightly cross-linking reaction to take place in the extruder.This method is illustrated in U.S. Pat. No. 3,250,731 with apolyfunctional azide, U.S. Pat. No. 4,714,716 (and publishedInternational Application WO 99/10424) with an azidofunctional silaneand EP 879,844-A1 with a peroxide in conjunction with a multi-vinylfunctional monomer. The aforementioned U.S. patents are incorporatedherein by reference. Irradiation techniques are illustrated by U.S. Pat.Nos. 5,605,936 and 5,883,151, which are also incorporated by reference.The polymer composition used to prepare the foam preferably has a gelcontent of less than 10 percent, more preferably less than 5 percent,per ASTM D2765-84, Method A.

If an ethylene polymer, such as the ethylene homopolymer, is blendedwith a propylene polymer, the weight ratio of the propylene polymer tothe ethylene polymer is preferably at least 35:65, more preferably atleast 1:1, preferably up to 9:1, and more preferably up to 7:1. Suchblends may optionally contain at least one substantially randominterpolymer, such as an ethylene/styrene interpolymer, as describedunder a separate heading below. An advantage of these foams is theability to use it in locations where a high service temperature isrequired and yet have a foam that is thermoformable and potentiallyrecyclable. An example is in the compartment of a motor, such as aninternal combustion engine, such as found on a vehicle, electricgenerator, compressor or pump. An indication of high service temperatureis resistance to heat distortion at elevated temperatures. As usedherein, the expression, “heat distortion temperature” refers to themaximum temperature at which the foam body does not shrink more than 5percent by volume during an exposure to that temperature for one hour.Preferably the heat distortion temperature of the foams according to thepresent invention is at least 130° C., more preferably at least 140° C.,and even more preferably at least 150° C.

B1) Graft-Modified Polymer of Polymer Matrix B)

At least one of the above-described polymers comprised in polymer matrixB) is graft-modified with at least one polar group selected from thegroup consisting of acids, acid salts, acid esters and acid anhydrides.The acid of the acid, acid ester, and acid anhydride, and salts thereof,is preferably a mono-unsaturated carboxylic acid. The mono-unsaturatedcarboxylic acid preferably contains at least 2, more preferably at least3, carbon atoms and preferably up to 50, more preferably up to 20, evenmore preferably up to 12, and even more preferably up to 8, carbonatoms. Examples include, but are not limited to, (meth)acrylic acid,(meth)acrylate esters, and maleic anhydride (also referred to herein as“MAH”). The grafted on polar group is generally a terminal or pendantgroup on the polymer chain(s) of the graft-modified polymer.

The presence and quantity of such functionality grafted to polymers maybe determined by those skilled in the analysis of polymers usingwell-known methods. Such methods may employ, for example, infraredspectroscopy (FTIR), nuclear magnetic resonance (NMR) spectroscopy, andchemical methods. Several such methods are described in detail in Part 4of the article by Moad cited below.

The synthesis of graft-modified polymers, especially graft-modifiedpolyolefin polymers and copolymers, is often carried out by reactiveextrusion. A widespread method for carrying out such reactive extrusioninvolves free radical-induced grafting. Such grafting typically involvescombining a free-radical initiator and a coagent with the polymer as thepolymer is conveyed through the extruder. Commonly used free-radicalinitiators include peroxides, such as dialkyl peroxides (for example,dicumyl peroxide). Commonly used coagents include monoene monomers and,for grafting polar groups onto propylene polymers, polyfunctionalmonomers such as triacrylate monomer in what is sometimes referred to as“novel reactive processing”. Coagents are generally used to improvegrafting yields by reducing side reactions.

Such synthesis processes are well known and are described, for example,in Stevens, Polymer Chemistry (Addison-Wesley, 1975) pp. 196-202, morerecently, in Moad, “The synthesis of polyolefin graft copolymers byreactive extrusion”, Prog. Polym. Sci. 24 (1999) 81-142, and in numerouspublished patents, some of which are cited in the respectivedescriptions of the acid, acid ester, and acid anhydride graft-modifedpolymers that follow. Typical synthesis examples are also described inEuropean Patent Number 188926, Belgian Patent Number 692301, JP27421/66, U.S. Pat. No. 3,499,819, and U.S. Pat. No. 5,137,975, whichare incorporated herein by reference.

Graft-modified polymers suitable for use in this invention may also bemade by polymer synthesis.

Suitable graft-modified materials are available commercially and areproduced by, for example, DuPont under BYNEL™ and FUSABOND®; BPPerformance Polymers, Inc., Hackettstown, N.J., U.S.A. under POLYBOND™(also available from Crompton Corporation); Mitsui Chemical Corporationunder ADMER™; Quantum under PLEXAR™; Elf Atochem under OREVAC™; MortonInternational under TYMOR™, which is made by Hercules and distributed byHimont under HERCOPRIME™ and distributed by Eastman under EPOLENE™; DSMunder YPAREX®; Hoechst AG under HOSTAMON™, Exxon Chemical underEXXELOR™; and The Dow Chemical Company under PRIMACOR®. These and othergraft-modified polymers may be combined, preferably blended, with theabove-described polymers which have not been graft-modified or whichhave been graft-modified to a lesser extent.

Graft modification may also be carried out in-situ before, during,and/or after combining the polymer resin components of the polymermatrix with the particulate additive(s) according to one or more of theabove-described grafting methods.

More detailed descriptions of preferred grafted polymers and preferredcombinations of such polymers with each other and with theabove-described polymers that are not graft-modified, which are suitablefor use in this invention, follows.

1. Acid-Modified Polymers

A suitable source of graft-modification are acids and their salts (forexample, metal salts, such as alkali metal salts). Preferred areunsaturated carboxylic acid monomers and their salts, especially thosehaving at least 3 carbon atoms up to 12 carbon atoms, more preferably upto 8 carbon atoms, and even more preferably up to 4 carbon atoms. Theacid monomers are preferably unsaturated aliphatic or cycloaliphaticgroups, which preferably have up to 8, more preferably up to 4, and evenmore preferably up to 2, carboxylic acid groups. Examples of suchmonomers include acrylic acid, methacrylic acid, maleic acid, fumaricacid, himic acid, itaconic acid, crotonic acid, isocrotonic acid,cinnamic acid, citraconic acid, mesaconic acid, maleic acid and succinicacid, combinations thereof, and salts thereof. In a preferredembodiment, at least one polymer is graft-modified with acrylic acidand/or methacrylic acid.

The acid monomers grafted onto the polymer may be present as pendant orterminal groups. Such pendant or terminal groups may be not only singleacid monomer groups, but also multiple acid monomer groups, which formpoly(acid) groups on the polymer chain(s) of the graft-modified polymer.Poly(acid) groups preferably contain at least 2, more preferably atleast 3, acid groups, and preferably up to 20, more preferably up to 12,and even more preferably up to 8, acid groups. Such poly(acid) groupsare generally, but not necessarily, the result of polymerization of atleast one of the above described acid monomers during the graftingprocess. The poly(acid) groups may also be partially or completelypre-polymerized prior to the grafting process. The polymerization may behomopolymerization of an acid monomer, or interpolymerization with oneor more additional acid monomers, and/or non-acid, monomers. In apreferred embodiment, the group grafted onto the polymer is acrylic acidor methacrylic acid and the resulting pendant groups are homopolymers ofmultiple acrylic acid groups or multiple methacrylic acid groups.

Pendant acid groups may be distinguished from polar groups copolymerizedinto the polymer chain(s) by the at least two carbon atoms of ahydrocarbylene moiety connecting the closest carbonyl moiety of the acidto the polymer chain. Copolymerized acid groups are generally connectedto the polymer chain by less than two carbon atoms from the closestcarbonyl atom of the acid moiety. This difference can be detected usingspectroscopic analysis, such as Fourier transform infrared spectroscopy(FTIR).

Processes for grafting such acids onto polymers are well known anddescribed in the patent and technical literature. Grafting of(meth)acrylic acid onto various polyolefin polymers is described, forexample, in U.S. Pat. No. 3,177,269; grafting of acrylic acid ontopolypropylene is described, for example, in GB-A-1,217,231; U.S. Pat.No. 3,862,265; U.S. Pat. No. 3,884,451; U.S. Pat. No. 3,953,655; U.S.Pat. No. 4,003,874; and U.S. Pat. No. 4,578,428; grafting of itaconicacid onto propylene polymers is described, for example, in U.S. Pat. No.4,694,031; grafting of acrylic acid onto ethylene-propylene copolymer isdescribed, for example, in GB-A-1,217,231; U.S. Pat. No. 3,953,655; U.S.Pat. No. 4,003,874; U.S. Pat. No. 4,260,690; and EP-A-33220; andgrafting of acrylic acid onto ethylene polymers described, for example,in U.S. Pat. No. 3,270,090; U.S. Pat. No. 4,003,874; U.S. Pat. No.4,260,690; U.S. Pat. No. 4,362,486; EP-A-33220; and U.S. Pat. No.4,739,017. Each of the aforementioned patents is incorporated herein byreference for their relevant disclosure.

Acid-modified polymers are commercially available from various sources.Acid-modified ethylene acrylate polymers (Series 2000) andacrylate-modified ethylene/vinyl acetate resins (Series 3100) areavailable from DuPont under BYNEL™.

2. Acid Ester-Modified Polymers

Another suitable source of graft-modification are acid esters and theirsalts (for example, metal salts, such as alkali metal salts, of partial,or half, esters). Preferred are esters of the above-described acidgroups, including the above-described mono(acids) and poly(acids), andparticularly esters of the above-described unsaturated carboxylic acids.The acid esters preferably have at least 3 carbon atoms and preferablyup to 24 carbon atoms, more preferably up to 8 carbon atoms, even morepreferably up to 4 carbon atoms, and even more preferably up to 4 carbonatoms, in each ester group. Acid esters derived from acids that containmore than one acid group may be partially or fully esterified. Partiallyesterified acid esters may thus contain both non-esterified acid groupsand esterified acid groups. The ester groups are preferably hydrocarbongroups, such as aliphatic (for example, alkyl) or cycloaliphatic (forexample, cycloalkyl) groups, and/or preferably comprise nonhydrocarbongroups such as glycidyl and/or amino groups.

Examples of such monomers include alkyl (meth)acrylates such as methylmethacrylate, ethyl methacrylate, hydroxyethyl methacrylate, n-butylacrylate, isobutyl acrylate and 2-ethylhexyl acrylate; (meth)acrylatescontaining non-hydrocarbon groups such as glycidyl (meth)acrylate,tert-butylaminoethyl (meth)acrylate, and dimethylaminoethyl(meth)acrylate; alkyl maleates, such as monoethylmaleate and diethylmaleate; alkyl fumerates, such as monomethyl fumerate and dimethylfumerate; and alkyl itaconates, such as monomethyl itaconate and diethylitaconate.

In one embodiment, the at least one polymer may be graft-modified withesters of di- and polyacids and their salts (for example, metal salts,such as alkali metal salts, of the half, or partial, esters). Examplesof suitable diacids include maleic acid, succinic acid and phthalicacid. Preferred maleates include dialkyl maleates, such as dimethyl,diethyl or dibutyl maleates. Polymers graft-modified with succinatesand/or maleates generally have single succinate and/or maleate groups asthe terminal or pendant groups on the polymer chain(s) of thegraft-modified polymer. The succinate or maleate moieties may beunsubstituted or substituted. Grafted on acid ester may be present onthe polymer chain as pendant and terminal acid ester groups. Pendantacid ester groups grafted onto the polymer may be distinguished fromacid ester groups copolymerized into the polymer chain(s) by the atleast two carbon atoms of a hydrocarbylene moiety connecting the closestcarbonyl moiety of the acid to the polymer chain. Copolymerized acidester groups are generally connected to the polymer chain by less thantwo carbon atoms from the closest carbonyl atom of the acid moiety. Thisdifference can be detected using spectroscopic analysis, such as FTIR.

Processes for grafting of various acid esters onto various polymers arewell known and described in the patent and technical literature (see,for example, U.S. Pat. No. 5,945,492). Grafting of methyl methacrylateand hydroxyethyl methacrylate onto polyolefins such as LDPE and EP isdescribed, for example, in EP-A-33,220; grafting of hydroxyethylmethacrylate onto propylene polymers is described, for example, in U.S.Pat. No. 5,086,112; grafting of glycidyl methacrylate onto propylenepolymers is described, for example, in U.S. Pat. No. 4,443,584 and U.S.Pat. No. 5,086,112. Graft-modification of LLDPE with dibutyl maleate isdescribed, for example, in U.S. Pat. No. 3,267,173. Each of theaforementioned patents is incorporated herein by reference.

Diallyl acids, such as diallyl maleate, may also be used as a coagentfor maleation of propylene polymers as described, for example, in U.S.Pat. No. 5,344,888, which is incorporated herein by reference.

Acid ester-modified polymers are commercially available from varioussources. Acrylate-modified ethylene/vinyl acetate resins (Series 3100),for example, are available from DuPont under BYNEL™.

3. Acid Anhydride-Modified Polymers

Another suitable source of graft-modification is acid anhydrides,especially diacid anhydrides, and their salts (for example, metal salts,such as alkali metal salts). Examples of acid anhydrides are MAH,citraconic anhydride, itaconic anhydride, nadic anhydride, and himicanhydride.

In a preferred embodiment, at least one polymer is graft-modified withMAH. MAH graft-modified polymers generally have succinic anhydrideand/or MAH, or oligomers thereof, as the terminal or pendant groups onthe polymer chain(s) of the graft-modified polymer, which upon exposureto moisture may to some extent be reversibly converted to succinic acidand/or maleic acid, or oligomers thereof. The succinic anhydride or MAHmoieties may be unsubstituted or substituted. The adjective “maleated”is used herein to indicate that the polymer has been graft-modified withmaleic anhydride. The verb “maleation” is used herein to refer tografting MAH onto a polymer.

Processes for maleation of polymers are well known and described in thepatent and technical literature. Maleation of polyolefin polymers isdescribed, for example, in U.S. Pat. No. 3,708,555; U.S. Pat. No.3,868,433; U.S. Pat. No. 3,882,194; U.S. Pat. No. 4,506,056; U.S. Pat.No. 4,751,270; U.S. Pat. No. 4,762,890; U.S. Pat. No. 4,857,254; U.S.Pat. No. 4,857,600; U.S. Pat. No. 4,927,888; U.S. Pat. No. 4,950,541;U.S. Pat. No. 5,945,492, each of which is incorporated herein byreference.

In particular, maleation of propylene homopolymers is described in U.S.Pat. No. 3,414,551; U.S. Pat. No. 4,753,997; U.S. Pat. No. 4,824,736;U.S. Pat. No. 4,857,254; U.S. Pat. No. 5,001,197; U.S. Pat. No.5,079,302; U.S. Pat. No. 5,344,886; U.S. Pat. No. 5,344,888; U.S. Pat.No. 5,945,492; U.S. Pat. No. 5,955,547; and U.S. Pat. No. 6,218,476,each of which is incorporated herein by reference. Maleation ofpropylene polymers is preferably carried out in the presence of styreneas the coagent as described, for example, in Labla et al., “MultiphasePolymers: Blends and Ionomers”, ACS Symposium Series 395, Chapt. 3, pp76-79 (1989). The pendant and/or terminal groups obtained via maleationusing a styrene coagent may be referred to as “styrene-MAH” and aresuitable for this invention.

Maleation of ethylene homopolymers, such as LDPE and HDPE, is describedin U.S. Pat. No. 3,873,643; U.S. Pat. No. 4,639,495; U.S. Pat. No.4,762,890; U.S. Pat. No. 4,788,264; U.S. Pat. No. 4,927,888; U.S. Pat.No. 4,987,190; and U.S. Pat. No. 5,945,492; maleation ofethylene-propylene copolymers is described in U.S. Pat. No. 5,001,197;U.S. Pat. No. 5,344,886; U.S. Pat. No. 5,344,888; U.S. Pat. No.5,367,022; and U.S. Pat. No. 5,552,096; and maleation of ethylene/C₃-C₂₀alpha-olefin interpolymers is described in U.S. Pat. No. 4,612,155; U.S.Pat. No. 4,739,017; U.S. Pat. No. 4,762,890; U.S. Pat. No. 4,857,254;U.S. Pat. No. 4,857,600; U.S. Pat. No. 4,927,888; U.S. Pat. No.5,180,788; U.S. Pat. No. 5,346,963; and U.S. Pat. No. 5,705,565. Each ofthe foregoing patents is incorporated herein by reference.

Acid anhydride-modified polymers are commercially available from varioussources. Anhydride-modified ethylene acrylate copolymers (Series 2100),anhydride-modified ethylene/vinyl acetate copolymers (Series 3000),anhydride-modified ethylene/vinyl acetate copolymers (Series 3800),anhydride-modified ethylene/vinyl acetate resins (Series 3900),anhydride-modified high density polyethylene resins (Series 4000),anhydride-modified linear low density polyethylene resins (Series 4100),anhydride-modified low density polyethylene resins (Series 4200), andanhydride-modified polypropylene resins (Series 5000) are available fromDuPont under BYNEL™. Maleated LLDPE is also available from QuantumChemical Corporation, Cincinnati, Ohio, U.S.A. under PLEXAR®, such asPLEXAR® PX360,3741 and 3779, from DSM under YPAREX™, such as YPAREX™8104E; and from Morton International; Chicago, Ill., U.S.A, underTYMOR®, such as TYMOR® 1203. Maleated polypropylene resins are alsoavailable from Quantum Chemical Corporation, Cincinnati, Ohio, U.S.A.under PLEXAR®, such as PLEXAR® 360, from Montell under QUESTRON™, suchas QUESTRON™ KA 805, from Mitsubishi Chemical Corporation under ADMER™,such as ADMER™ QF305 and ADMER™ QF500, from Elf Atochem under OREVAC™,such as PP-FT or PP-C, from Montell USA Inc. under HERCOPRIME™, such asHERCOPRIME™ HG201 or G211, and from Eastman Chemicals under EPOLENE™,such as EPOLENE™ E43, G3003 and G3015.

B2) Composition of Polymer Matrix B)

The polymer matrix for making the cellular thermoplastic foam comprisesat least one polymer resin comprising multiple polymer moleculesgraft-modified with, on the average, at least one polar group accordingto the above description of graft-modification. The polymer matrix maycomprise one polymer or several different polymers in admixture, such asin a blend, with each other.

When more than one polymer is present in the polymer matrix, the polymermatrix may comprise (1) one or more polymer resins comprising multiplepolymer molecules graft-modified with, on the average, at least onepolar group per above (“first category”) combined with (2) one or moredifferent polymer resins which are not graft-modified, graft-modified toa different degree, or graft-modifed with different polar groups(“second category”). In a preferred embodiment, the at least one firstcategory polymer resin comprises at least one polymer resin that has, onthe average, at least one, preferably at least two, polar groups perresin molecule and the at least one second category polymer resin has,on the average, less than one, more preferably less than 0.1, and evenmore preferably less than 0.01, and even more preferably zero, polargroup per polymer resin molecule.

In a preferred embodiment, the polymer resin comprises at least onepolyolefin resin, especially a thermoplastic polyolefin resin. The atleast one polyolefin resin preferably comprises at least one ethylenepolymer, at least one propylene polymer, or a mixture of at least oneethylene polymer with at least one propylene polymer. At least onepolyolefin resin preferably has on the average less than one, morepreferably less than 0.1, and more preferably less than 0.01, and evenmore preferably zero, polar group per polymer resin molecule.

In the case of combinations of polymer resins, the polymer resins arepreferably in the form of a blend. To form such blends, the polymerresins preferably have similar melt flow rates measured according toASTM D1238, which unless stated otherwise is measured under a forceapplied by 2.16 kg,. The ratio of the melt flow rate of the polymerresin having the lowest melt flow rate to the melt flow rate of thepolymer resin having the highest melt flow rate is preferably at least1:20, more preferably at least 1:10, even more preferably at least 1:4,and even more preferably at least 1:3, and even more preferably at least1:2 and preferably up to 20:1, more preferably up to 10:1, and even morepreferably up to 3:1. When the combination of polymer resins is amixture of at least one ethylene polymer with at least one propylenepolymer, the ratio of the melt index of the ethylene polymer to the meltflow rate of the propylene polymer is preferably at least 1:4, morepreferably at least 1:3, and even more preferably at least 1:2, andpreferably up to 20:1, more preferably up to 10:1, and even morepreferably up to 3:1.

The polymer matrix preferably comprises at least 0.01, more preferablyat least 0.05, more preferably at least 0.1, and even more preferably atleast 1, weight-percent polar groups and preferably up to 20, morepreferably up to 10, and even more preferably up to 6, weight-percentpolar groups. In a preferred embodiment, the polymer matrix comprises acombination of polymer resins wherein at least one, more preferably one,of the polymer resins has a weight-percent amount of polar groups withinthe above weight-percent ranges. In the latter case, the polymer resinshaving polar groups preferably comprise at least 0.5, more preferably 1,and even more preferably 2, weight-percent, and preferably up to 20,more preferably up to 10, and even more preferably up to 5,weight-percent, based on the total weight of the polymer resins in thepolymer matrix.

The polymer resin material is combined with the particulate additive toform the polymer matrix. The particulate additive is preferably mixedwith the polymer resins until the particulate additive is homogeneouslydispersed in the polymer resin material. In the preferred polymer matrixcomprising a combination of polymer resins, the particulate additive isfirst combined, preferably admixed, with at least one polymer resingrafted with polar groups in one of the preferred amounts, such as theamounts preferred for the first category polymer resins described above,to form a concentrate, which is then combined, preferably blended, withat least one, preferably more than one, polymer resin of the polymermatrix which contains a lower ratio of, or zero, polar groups perpolymer molecule, such as one or more of the second category polymerresins described above.

The weight-ratio of the polymer resins having polar groups to theparticulate additive is preferably at least 0.1:1, more preferably atleast 0.25:1, and even more preferably at least 0.5:1, and preferably upto 5:1, more preferably up to 2:1, and even more preferably up to 1:1.The total amount of particulate additive in the polymer matrix ispreferably at least 0.5, more preferably 1, and even more preferably 2,weight-percent, and preferably up to 10, more preferably up to 7, andeven more preferably up to 5, weight-percent, based on the total weightof the polymer resins in the polymer matrix.

C) Organic Flame Retardant

The foams of the invention preferably include an organic flame retardantnot included, but rather in addition to, the above particulate additivesA), which functions to slow or minimize the spread of fire in the foam.The flame retardant is preferably a halogen-containing compound ormixture of compounds which imparts flame resistance to the foams of thepresent invention.

The term “halo” or “halogenated” includes compounds containing bromine,chlorine, or fluorine, or any combination thereof. Preferably, the flameretardant is a bromine or chlorine-containing compound. They may behalogenated aromatic or alkane compounds.

Suitable aromatic halogenated flame retardants are well-known in the artand include but are not limited to hexahalodiphenyl ethers,octahalodiphenyl ethers, decahalodiphenyl ethers, decahalodiphenylethanes; 1,2-bis(trihalophenoxy)ethanes;1,2-bis(pentahalophenoxy)ethanes; a tetrahalobisphenol-A;ethylene(N,N′)-bis-tetrahalophthalimides; tetrabromobisphenol Abis(2,3-dibromopropyl ether); tetrahalophthalic anhydrides;hexahalobenzenes; halogenated indanes; halogenated phosphate esters;halogenated polystyrenes; and polymers of halogenated bisphenol-A andepichlorohydrin, and mixtures thereof. Preferred aromatic halogenatedflame retardants may include one or more of tetrabromobisphenol-A(TBBA), tetrabromo bisphenol A bis(2,3-dibromopropyl ether),decabromodiphenyl ethane, brominated trimethylphenylindane, or aromatichalogenated flame retardants with similar kinetics.

Suitable halogenated alkane compounds may be branched or unbranched,cyclic or acyclic. Preferably, the halogenated alkane compound iscyclic. Suitable halogenated alkane flame retardants include and are notlimited to hexahalocyclododecane; tetrabromocyclooctane;pentabromochlorocyclohexane;1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane; 1,1,1,3-tetrabromononane;and mixtures thereof. Preferred halogenated alkane flame retardantcompounds include hexabromocyclododecane and its isomers,pentabromochlorocyclohexane and its isomers, and1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane and its isomers.Hexabromocyclododecane (HBCD), and halogenated alkane flame retardantswith similar kinetics are preferred.

Commercially available products suitable for use as flame retardants inthe present invention include PE-68™ (a trademark and product of theGreat Lakes Chemical Corporation). Suitable flame retardants are wellknown, and include brominated organic compounds such as are described inU.S. Pat. No. 4,446,254 and U.S. Pat. No. 5,171,757, which areincorporated herein by reference. For foams, the halogen contentprovided by the halogenated flame retardants in the final foams shouldbe 0.05-20 phr, preferably 0.1-15 phr and most preferably 0.5-15 phr.

The polymeric resin compositions preferably include at least about 0.5phr halogenated flame retardant, more preferably at least about 0.8 phr,preferably up to about 12 phr, more preferably up to about 6 phrhalogenated flame retardant. The parts per hundred parts of resin(“phr”) are based on the total parts by weight of polymer in the flameretardant-containing composition.

In a preferred embodiment, the flame retardant is ahexahalocyclododecane, preferably hexabromocyclododecane (HBCD), ortetrabromobisphenol A bis(2,3-dibromopropyl ether), PE™-68, or acombination with any other halogenated or non-halogenatedflame-retardants, which can include, but are not limited to phosphorousbased flame retardants such as triphenyl phosphate and encapsulated redphosphorous.

In a preferred embodiment, the flame retardant is a mixture of at leasttwo different types of flame retardants that may be added together orseparately into a polymer resin composition. A mixture that includesboth a halogenated alkane compound and an aromatic halogenated compoundhas been found to enhance blending of α-olefin polymers with alkenylaromatic polymers which are described in more detail under separateheadings below, and this combination tends to reduce the density offoams made from that mixture. The ratio of aromatic halogenated flameretardant to halogenated alkane flame retardant in parts by weight forthat purpose is preferably from about 16:1 to 1:16, more preferably fromabout 7.5:1 to 1:7.5, and most preferably about 5:1 to 1:5. Theconcentration of aromatic halogenated flame retardant is preferably atleast about 0.5 parts by weight per hundred parts by weight (phr) of theα-olefin polymer component, more preferably at least 1 phr, andpreferably up to 8 phr based on the weight of the α-olefin polymercomponent. The concentration of halogenated alkane flame retardant ispreferably at least about 0.5 parts by weight per hundred parts byweight (phr) of the alkenyl aromatic polymer component, more preferablyat least 1 phr, and preferably up to 8 phr based on the weight of thealkenyl aromatic polymer component. In a preferred embodiment, the flameretardant mixture includes a combination of hexahalocyclododecane suchas hexabromocyclododecane (HBCD), and tetrabromobisphenol Abis(2,3-dibromopropyl ether).

The organic flame retardants C) are preferably combined with theabove-described flame retardant adjuvant. Combinations of organic flameretardants C) with the above-described flame retardant synergists areparticularly preferred.

Synergistic combinations, such as mixtures of one or more halogenatedcompounds and one or more flame retardant synergists, typically are usedpreferably at a ratio of 0.25 to 25, preferably 0.5 to 15, morepreferably from 0.5 to 12 parts by weight flame retardant halogen to 1part by weight of flame retardant synergist. In the case of anantimony-containing synergist, the ratio of halogen contained in thehalogenated flame retardant to antimony contained in the flame retardantsynergist is preferably in the range from 1 to 7 moles, more preferably1 to 6 moles, and even more preferably 1 to 4 moles, halogen contributedby the flame retardant per one mole antimony contributed by the flameretardant synergist.

D) Stability Control Agent or Cell Size Enlarging Agent

A stability control agent or cell size enlarging agent is optionallyadded to the present foam to enhance dimensional stability. Preferredagents include amides and esters of C₁₀₋₂₄ fatty acids. Such agents areseen in U.S. Pat. No. 3,644,230 and U.S. Pat. No. 4,214,054, which areincorporated herein by reference. Most preferred agents include stearylstearamide, glycerol monostearate (available from ICI Americas Inc.,under the trademark Atmer™ 129), glycerol monobehenate, and sorbitolmonostearate. Typically, such stability control agents are employed inan amount ranging from 0.1 to 10 phr.

E) Other Additives

The foam of the present invention may optionally contain one or moreconventional additives different from, and in addition to, theabove-described additives to the extent that they do not interfere withthe desired foam properties. Typical additives include organic flameretardant synergists, such as dicumyl(dimethyldiphenylbutane),poly(1,4-diisopropyl-benzene), halogenated paraffin, triphenylphosphate,and mixtures thereof, antioxidants such as hindered phenols andphosphites (for example, IRGANOX™ 1010 and IRGAFOS™ 168, respectively,each a trademark of and available from the Ciba Geigy Corporation),ultraviolet stabilizers such as hindered amine light stabilizers (forexample TINUVIN™ 770, which is a trademark of and available from theCiba Geigy Corporation), cling additives (for example, polyisobutylene),organic colorants, and extrusion aids.

Preparation of Foams

The foam structure of the invention may be prepared by conventionalextrusion foaming processes. This process generally entails feeding theingredients of the polymeric resin composition together or separatelyinto the heated barrel of an extruder, which is maintained above thecrystalline melting temperature or glass transition temperature of theconstituents of the polymeric resin composition; heating the polymericresin composition to form a plasticized or melt polymer material;incorporating a blowing agent into the melt polymer material to form afoamable gel; and expanding the foamable gel to form the foam product.The foamable gel may be extruded or conveyed through a die of desiredshape to an area of lower pressure where the mixture expands to form acellular foam structure. The lower pressure is preferably at anatmospheric level. Typically, the mixture is cooled to within +/−20° C.of the highest crystalline melting point or glass transition temperatureof the components of the polymeric resin composition before extrusion inorder to optimize physical characteristics of the foam.

Processes for making polyolefin foam structures are described in C. P.Park. “Polyolefin Foam”, Chapter 9, Handbook of Polymer Foams andTechnology, edited by D. Klempner and K. C. Frisch, Hanser Publishers,Munich, Vienna, New York, Barcelona (1991) and in WO 00/15697; WO00/15700; WO 01/70860; WO 01/70861; and WO 01/70479, which areincorporated herein by reference.

A preferred process involves using a low die pressure for extrusionwhich is greater than the prefoaming critical die pressure but only ashigh as four times, more preferably three times, even more preferablytwo times, the prefoaming critical die pressure. The prefoaming criticaldie pressure is best determined experimentally for formulationscomprising not only the polymer components but also additional additivessuch as flame retardants, synergists and cell enlarging agents. This istypically accomplished by preparing foams at several prefoaming diepressures and determining the effect of changes in the die pressure onthe foam cell size and appearance. Below the prefoaming critical diepressure, the quality of the foam deteriorates sharply, rough skin isobserved on the foam due to rupture of surface cells and typically acrackling noise is heard at the die due to rapid degassing of theblowing agent. At too high die pressures, the foam tends to nucleatesignificantly causing a loss in cell size upper limit which typicallycorresponds to a value of up to four times, the prefoaming critical diepressure.

In a preferred embodiment of the present invention, the resulting foamstructure is optionally formed in a coalesced strand form by extrusionof the foamable gel through a multi-orifice die. The orifices arearranged so that contact between adjacent streams of the moltenextrudate occurs during the foaming process and the contacting surfacesadhere to one another with sufficient adhesion to result in a unitaryfoam structure. The streams of molten extrudate exiting the die take theform of strands or profiles, which desirably foam, coalesce, and adhereto one another to form a unitary structure. Desirably, the coalescedindividual strands or profiles should remain adhered in a unitarystructure to prevent strand delamination under stresses encountered inpreparing, shaping, and using the foam. Apparatuses and method forproducing foam structures in coalesced strand form are seen in U.S. Pat.No. 3,573,152 and U.S. Pat. No. 4,824,720, both of which areincorporated herein by reference.

Alternatively, the resulting foam structure is conveniently formed by anaccumulating extrusion process as seen in U.S. Pat. No. 4,323,528, whichis incorporated by reference herein. In this process, low density foamstructures having large lateral cross-sectional areas are preparedby: 1) forming under pressure the foamable gel from a polymeric resincomposition and a blowing agent at a temperature at which the viscosityof the gel is sufficient to retain the blowing agent when the gel isallowed to expand; 2) extruding the gel into a holding zone maintainedat a temperature and pressure which does not allow the gel to foam, theholding zone having an outlet die defining an orifice opening into azone of lower pressure at which the gel foams, and an openable gateclosing the die orifice; 3) periodically opening the gate; 4)substantially concurrently applying mechanical pressure by a movable ramon the gel to eject it from the holding zone through the die orificeinto the zone of lower pressure, at a rate greater than that at whichsubstantial foaming in the die orifice occurs and less than that atwhich substantial irregularities in cross-sectional area or shapeoccurs; and 5) permitting the ejected gel to expand unrestrained in atleast one dimension to produce the foam structure.

Blowing agents useful in making the resulting foam structure includeinorganic agents, organic blowing agents and chemical blowing agents.Suitable inorganic blowing agents include carbon dioxide, nitrogen,argon, water, air, nitrogen, and helium. Organic blowing agents includealiphatic hydrocarbons having 1-9, preferably 1-6, carbon atoms,aliphatic alcohols having 1-3 carbon atoms, and fully and partiallyhalogenated aliphatic hydrocarbons having 1-4 carbon atoms. U.S. Pat.No. 6,048,909 to Chaudhary et al. discloses a number of suitable blowingagents at column 12, lines 6-56, the teachings of which are incorporatedherein by reference. Preferred blowing agents include aliphatichydrocarbons having 1-9 carbon atoms, especially propane, n-butane andisobutane, more preferably isobutane.

The amount of blowing agent incorporated into the polymer melt materialto make a foamable gel is preferably from 0.2 to 5.0, more preferablyfrom 0.5 to 3.0, and even more preferably from 1.0 to 2.50 gram molesper kilogram of polymer. However, these ranges should not be taken tolimit the scope of the present invention.

The foam is conveniently extruded in various shapes having a preferredfoam thickness in the direction of minimum foam thickness in the rangefrom about 1 mm to about 100 mm or more. When the foam is in the form ofa sheet, the foam preferably has a thickness in the range from about 1or 2 mm to about 15 mm. When the foam is in the form of a plank, thefoam preferably has a thickness in the range from about 15 mm to about100 mm. The desired thickness depends in part on the application.

When the foam of this invention is a thick sheet or plank, the foamdesirably has perforation channels. Thick polymer foams may have anaverage thickness perpendicular to the surface perforated of at leastabout 25 millimeters (mm) and the polymer foam may be preferablyperforated to an average depth of at least 5 mm below the surface of thepolymer foam. Typically, perforation comprises puncturing the base foam.A description of how to create suitable perforation channels toaccelerate release of blowing agent from the foam is provided in U.S.Pat. No. 5,585,058, which is incorporated herein by reference.Accelerated aging of the foam to remove blowing agent may also beachieved, for example, by perforation techniques and heat aging asdescribed in U.S. Pat. No. 5,242,016 and U.S. Pat. No. 5,059,376, whichare also incorporated herein by reference. Perforation of macrocellularfoams to improve acoustic performance of thermoplastic foams isdescribed in WO 00/15697, which is also incorporated herein byreference.

The foam of this invention preferably has perforation channels, morepreferably a multiplicity of perforation channels extending from the atleast one surface into the foam such that there is an average of atleast one, preferably at least 5, more preferably at least 10, even morepreferably at least 20, and even more preferably at least 30,perforation channel(s) per 10 square centimeters (cm²) area of the atleast one surface. The term “multiplicity” as used herein means at leasttwo. In a preferred embodiment, the foam of this invention contains atleast seven perforation channels.

The perforation channels preferably have an average diameter at the atleast one surface of at least 0.1 mm, more preferably at least 0.5 mm,and even more preferably at least 1 mm and preferably up to about theaverage cell size of the foam measured according to ASTM D3756. One ormore surfaces of the foam preferably has an average of at least fourperforation channels per square centimeter extending from the at leastone surface into the foam.

The polymer foam preferably has an average thickness perpendicular tothe surface perforated of at least 25 mm and the polymer foam ispreferably perforated to an average depth of at least 5 mm below thesurface of the polymer foam.

Typically, perforation comprises puncturing the base foam with one ormore pointed, sharp objects. Suitable pointed, sharp objects includeneedles, spikes, pins, or nails. In addition, perforation may comprisedrilling, laser cutting, high pressure fluid cutting, air guns, orprojectiles.

In addition, the base foam may be prepared to have elongated cells bypulling the foam during expansion. Such pulling results in elongatedcells without changing or often, increasing the cell size in thehorizontal direction. Thus, pulling results in an increased average cellsize in the direction perpendicular to the vertical direction (EHaverage) and facilitates perforation.

Perforation of the base foam may be performed in any pattern, includingsquare patterns and triangular patterns. Although the choice of aparticular diameter of the sharp, pointed object with which to perforatethe base foam is dependent upon many factors, including average cellsize, intended spacing of perforations, pointed, sharp objects useful inthe preparation of certain foams of the present invention will typicallyhave diameters of from 1 mm to 4 mm.

Compression may be used as an additional means of opening cells.Compression may be performed by any means sufficient to exert externalforce to one or more surfaces of the foam, and thus cause the cellswithin the foam to burst. Compression during or after perforation isespecially effective in rupturing the cell walls adjacent to thechannels created by perforation since a high pressure difference acrossthe cell walls can be created. In addition, unlike needle punching,compression can result in rupturing cell walls facing in all directions,thereby creating tortuous paths desired for sound absorption.

The mechanical opening of closed-cells of the base foam lowers theairflow resistivity of the base foam by creating large-size pores in thecell walls and struts. In any event, regardless of the particular meansby which it does so, such mechanical opening of closed-cells within thebase thermoplastic polymer foam serves to enhance the usefulness of thefoam for sound absorption and sound insulation applications.

Of course, the percentage of cells opened mechanically will depend on anumber of factors, including cell size, cell shape, means for opening,and the extent of the application of the means for opening applied tothe base foam.

The resulting foam structure preferably exhibits good dimensionalstability. Preferred foams recover 80 or more percent of initial volumewithin a month with initial volume being measured within 30 secondsafter foam expansion. Volume is measured by a suitable method such ascubic displacement of water.

In one embodiment, the foam structure may be substantially cross-linked.Cross-linking may be induced by addition of a cross-linking agent or byradiation. Induction of cross-linking and exposure to an elevatedtemperature to effect foaming or expansion may occur simultaneously orsequentially. If a cross-linking agent is used, it is incorporated intothe polymer material in the same manner as the chemical blowing agent.Further, if a cross-linking agent is used, the foamable melt polymermaterial is heated or exposed to a temperature of preferably less than150° C. to prevent decomposition of the cross-linking agent or theblowing agent and to prevent premature cross-linking. If radiationcross-linking is used, the foamable melt polymer material is heated orexposed to a temperature of preferably less than 160° C. to preventdecomposition of the blowing agent. The foamable melt polymer materialis extruded or conveyed through a die of desired shape to form afoamable structure. The foamable structure is then cross-linked andexpanded at an elevated or high temperature (typically, 150° C.-250° C.)such as in an oven to form a foam structure. If radiation cross-linkingis used, the foamable structure is irradiated to cross-link the polymermaterial, which is then expanded at the elevated temperature asdescribed above. The present structure can advantageously be made insheet or thin plank form according to the above process using eithercross-linking agents or radiation.

Crosslinked acoustically active thermoplastic macrocellular foams andmethods for manufacturing them are described in more detail in WO00/15700, which is incorporated herein by reference.

The present foam structure may also be made into a continuous plankstructure by an extrusion process utilizing a long-land die as describedin GB 2,145,961A. In that process, the polymer, decomposable blowingagent and cross-linking agent are mixed in an extruder, heating themixture to let the polymer cross-link and the blowing agent to decomposein a long-land die; and shaping and conducting away from the foamstructure through the die with the foam structure and the die contactlubricated by a proper lubrication material

In a preferred embodiment of the present invention, the macroccllularthermoplastic polymer foams have less than 35 percent crosslinking after10 days aging. The resulting foam structure more preferably has not morethan 30 percent crosslinking, even more preferably less than 20 percentcrosslinking, and even more preferably less than 10 percentcrosslinking, after 10 days aging. The foam of this invention is evenmore preferably substantially noncrosslinked or uncrosslinked and thepolymer material comprising the foam structure is preferablysubstantially free of crosslinking.

The resulting foam structure may be either closed-celled or open-celled.The open cell content will range from 0 to 100 volume-percent asmeasured according to ASTM D2856-A. In one embodiment, the foamstructure has an open cell content not greater than 30 volume-percent,more preferably not greater than 20 volume-percent, measured accordingto that ASTM method.

The resulting foam structure preferably has a density of less than 300,preferably less than 100, more preferably less than 60 and mostpreferably from 10 to 50 kilograms per cubic meter.

The macrocellular foams exhibit an average cell size of at least 1.5 mm,preferably 2 mm, more preferably at least 3 mm, even more preferably atleast 4 mm, preferably up to 20 mm, 15 mm and 10 mm also beingpreferred, according to ASTM D3575.

Properties and End Uses

Applications for the macrocellular flame resistant acoustic compositionsof the present invention include articles made by all the variousextrusion processes. Such articles may be used in automotive and othertransportation devices, building and construction, household and gardenappliances, power tool and appliance and electrical supply housing,connectors, and aircraft as acoustic systems for sound absorption andinsulation. The materials are especially suited to applications where,in addition to meeting the relevant acoustic performance standards, theymust also meet any applicable fire test codes, for example officepartitions, automotive decouplers, domestic appliance sound insulation,and sound proofing panels and machine enclosures. The ability to passthe US FMVSS 302 (auto) test, have a US Underwriter's Laboratory UL 94rating of HF1, and a B1 rating under German norm DIN 4102 are some ofthe goals that may be achieved with the present invention.

The foams of the present invention have excellent acoustic absorptioncapabilities. One way to measure the ability to absorb sound is tomeasure the acoustic absorption coefficient of the foam according toASTM E1050 at sound frequencies of 250, 500, 1000 and 2000 Hz and thencalculate the arithmetic average of those sound absorption coefficients.When that determination is made with the foams of the present invention,the average sound absorption coefficient is greater than 0.15,preferably greater than 0.20, more preferably greater than 0.25, evenmore preferably greater than 0.30. Thus the foams of this invention areuseful for absorbing sound in the range from 250 to 2000 Hz such thatthe sound absorption capability is equivalent to the foregoing preferredaverage sound absorption coefficients. For example, the foam may belocated in the presence of a sound intensity of at least 50 decibels,such as on a vehicle equipped with a combustion engine. Unexpectedly,foams of the present invention have a peak absorption coefficient of atleast 0.5 within a frequency range of 250 to 1000 Hz for foams having athickness within a range of from 10 nm to 100 mm.

Another advantage of the foam of the present invention is that the highaverage sound absorption coefficient may be achieved with a low waterabsorption. That is desirable to help limit corrosion of proximate metalparts, to avoid the growth of bacteria and mold, and to improve thermalinsulation value where that is needed. The inventive foam preferablydoes not absorb more than 10 percent water by volume, 5 percent water byvolume, 3 percent water by volume, more preferably not more than 1.5percent water by volume, and even more preferably not more than 1percent water by volume, when measured according to European Norm (EN)12088 at a 50° C. temperature gradient between a warm, water-saturatedatmosphere and the foam (the latter of which is maintained at atemperature at or below about 0° C. in order to condense the water ontothe surface of the foam sample) based on a test period of 14 daysexposure.

The foregoing list merely illustrates a number of suitable applications.Skilled artisans can readily envision additional applications withoutdeparting from the scope or spirit of the present invention.

The following examples illustrate, but do not in any way limit the scopeof the present invention.

EXAMPLES

Materials Used to Prepare the Foams of the Examples:

-   1. LDPE 620i is a low density polyethylene (LDPE) with a density of    0.924 g/cc and melt index of 1.8 dg/min (according to ASTM D1238,    190° C./2.16 kg) available from the Dow Chemical Company.-   2. PROFAX™ PF814 is a high melt strength polypropylene (HIMS PP)    with a melt index of 3 dg/min (according to ASTM D1238, 230° C./2.16    kg) available from Montell Polyolefins.-   3. TRUTINT™ 50 is antimony trioxide synergist, Sb2O3, of average    particle size of 3.0 microns, respectively (used as an 80%    concentrate in LDPE 620i) and is a trademark of and available from    the Great Lakes Chemical Corporation.-   4. MICROFINE™ AO-3 is antimony trioxide (Sb2O₃) synergist having an    average particle size of 0.3 microns (used as an 80% concentrate in    LDPE 620i) and is a trademark of and available from the Great Lakes    Chemical Corporation.-   5. BYNEL™ 4206 is MAH-modified LDPE having a melt index of 2.5 dg/10    min. (according to ASTM D 1238, 190° C./2.16 kg), a melting point of    102 degrees Celsius, and a Vicat softening point of 75 degrees    Celsius (according to ASTM D 1525), available from E.I. du Pont de    Nemours, Wilmington, Del.-   6. FP Black D29045 PEC is 50 weight-percent carbon black in LDPE    620i available from Technical Polymer Representatives, Inc.-   7. PE-68™ is a brominated fire retardant having 68 wt % bromine    content (tetrabromobisphenol A bis(2,3-dibromopropyl ether) as a 30%    concentrate in LDPE 620i). It is a trademark of, and available from,    the Great Lakes Chemical Corporation.-   8. SAYTEX™ HP-900 is hexabromocyclododecane (HBCD), a brominated    fire retardant containing about 75 wt % bromine. It is a trademark    of and available from the Albemarle Corporation.-   9. ATMER™ 129 is glycerol monostearate (GMS), a permeability    modifier/cell size enlarger, (used as an 10% concentrate in LDPE    620i) and is a trademark of and available from ICI Americas.-   10. IRGANOX™ 1010 is a phenolic antioxidant/stabilize. It is a    trademark of and available from Ciba Specialty Chemicals-   11. ULTRANOX™ 626 is a phosphite antioxidant/stabilizer and is a    trademark of, and available from, GE Specialty Chemicals

Tests for the examples below were conducted by extruding theformulations specified in the respective Tables 1 to 3 on an extrusionline. The extrusion line consists of a twin screw extruder with feedingzones for resins and solid additives, melting zones, and metering zones.In addition, there are mixing zones with ports for injecting blowingagents and liquid additives and a cooling zone to uniformly cool themelt to the foaming temperature. The foaming temperature is the optimalgel temperature for foaming when the melt strength is high enough tostabilize the foam and prevent cell collapse. The line also consists ofa gear pump between the metering and mixing zones to stabilize the meltflow and a static mixer in the cooling zone to aid in gel temperatureuniformity. The melt is extruded through a die to ambient temperatureand pressure to expand the gel to the desired shape and stabilize thefoam.

Example 1

The formulations shown in Table 1 below are run on a twin screwextrusion line maintained at polyethylene processing conditions. In eachrun, the foaming temperature is 110° C. and the pressure at the die ismaintained within the range of 250-300 psi (17-21 bar or 1.72-2.07 MPa).The levels of the additives used in the formulation (irrespective ofwhether they are fed as powders or as concentrates) are reported on anactive basis in phr (parts by weight per hundred parts by weight ofpolymer). The level of blowing agent used in the formulation is reportedin pph (parts by weight per hundred parts by weight total feed, that ispolymer and additives).

For Formulation 1 according to this invention, a concentrate is preparedby separately and preliminarily combining 10 parts by weight of theTRUTINT™ 50 antimony trioxide concentrate with 8 parts by weight of theBYNEL™ 4206 maleated LDPE in 20 parts by weight of LDPE 620i in a twinscrew compounder under the same temperature pressure conditions as formaking the foams stated above. The concentrate is introduced into thesame extruder used to make the foams with Formulation Control 1 andFormulation Comparative 1 to provide the parts per hundred parts byweight resin (pph) of TRUTINT™ 50 and BYNEL™ 4206 specified in Table 1for Formulation 1. Since the concentrate contributes to the total LDPE620i, the balance of the LDPE 620i introduced into the latter extruderto make the foam of Formulation 1 is reduced to maintain a total LDPE620i rate of 100 pph.

The average cell size of the respective foams made with each formulationis shown in Table 1.

TABLE 1 SAYTEX ™ TRUTINT ™ Average cell Formulation* HP-900 PE-68 ™ 50BYNEL ™ 4206 size Control 1 0 pph 0 pph 0 pph 0 pph 10.0 mm Comparative1 6 pph 3 pph 3 pph 0 pph  2.8 mm 1 6 pph 3 pph 3 pph 3 pph  7.5 mm*Other ingredients in each Run formulation: PE 620i: 100 pph; Irganox ™1010: 0.3 phr; Atmer 129: 0.5 phr; isobutane as blowing agent: 9 pph

As can be seen from the data in Table 1, when the concentrate containingBYNEL™ 4206 is purged in, the cell size of the foam increased from 2.8mm to 7.5 mm, representing a 168% increase relative to the comparativefire retardant (FR) formulation containing untreated TRUTINT™ 50antimony trioxide. Larger cell size provides improved acousticperformance.

Example 2

The formulations shown in Table 2 below are run on a twin screwextrusion line under the same conditions as in Example 1. ForFormulation 2 according to this invention, a concentrate is prepared inthe same way as in Example 1, except that MICROFINE™ AO-3 antimonytrioxide is substituted for TRUTINT™ 50.

The average cell size of the respective foams made according to each runis shown in Table 2.

TABLE 2 SAYTEX ™ MICROFINE ™ Average cell Formulation* HP-900 PE-68 ™AO-3 BYNEL ™ 4206 size Control 2 0 pph 0 pph 0 pph 0 pph 10.0 mmComparative 2 6 pph 3 pph 3 pph 0 pph  6.5 mm 2 6 pph 3 pph 3 pph 3 pph 8.0 mm *Other ingredients in each Run formulation: PE 620i: 100 pph;Irganox ™ 1010: 0.3 phr; Atmer 129: 0.5 phr; isobutane as blowing agent:9 pph

As can be seen from the data in Table 2, when the concentrate containingBYNEL™ 4206 is purged in, the cell size of the foam increased from 6.5mm to 8.0 mm, representing a 23 percent increase relative to thecomparative FR formulation containing untreated MICROFINE™ AO-3 antimonytrioxide. The larger cell size improves acoustic performance, especiallyin the low frequency range, such as at 250 and 500 hertz (Hz).

Example 3

The formulations shown in Table 3 below are run on a twin screwextrusion line maintained at polypropylene processing conditions. Ineach run, the foaming temperature is 147° C. and the pressure at the dieis maintained within the range of 350400 psi (24-28 bar or 2.41-2.76MPa).

In this case, BYNEL™ 4206 maleated LDPE is not first combined withMICROFINE™ AO-3 as in Examples 1 and 2. Instead, it is added directly tothe extruder used make the foam to treat the MICROFINE™ AO-3 in situdirectly within that extruder.

The average cell size of the respective foams made with each formulationis shown in Table 3.

TABLE 3 Average Formu- MICROFINE ™ cell lation* PE-68 ™ AO-3 BYNEL ™4206 size Control 0 pph   0 pph   0 pph  9.5 mm 3 Compar- 5 pph 2.5 pph  0 pph  8.8 mm ative 3 3 5 pph 2.5 pph 3.2 pph 10.1 mm *Otheringredients in each Run formulation: PROFAX ™ PF-814 HMS PP: 60 pph;PE-620i LDPE: 40 pph; IRGANOX ™ 1010: 0.5 phr; ULTRANOX ™ 626: 0.2 phr;ATMER 129GMS: 0.5 phr; FP Black D29045 PEC: 0.375 phr; and isobutane asblowing agent: 8 pph

As can be seen from the data in Table 3, when the concentrate containingBYNEL™ 4206 is purged in, the cell size of the foam increased from 8.8mm to 10.1 mm, representing a 15 percent increase relative to thecomparative fire retardant (FR) formulation containing untreatedMICROFINE™ AO-3 antimony trioxide. The larger cell size improvesacoustic performance, especially in the low frequency range such as at250 and 500 hertz (Hz).

In addition, Comparative Formulation 3 produces a foam having extremelysmall cells at the skin surface of the extruded and expanded foam (thesurfaces that come in contact with the die during extrusion). Whenmaleated LDPE is added in Formulation 3 according to the invention, thecell size at the skin surface increases substantially. This results in afurther improved acoustic performance of the foam having the skin layerdue to the presence of large cells at the surface which is exposed toacoustic vibrations.

1. A macrocellular polymer foam having an average cell size, measuredaccording to ASTMD3575, of at least 1.5 mm and a density less than 100kilograms per cubic meter comprising: A) at least one particulateadditive in admixture with B) a polymer matrix, wherein the polymermatrix comprises at least one polymer resin graft-modified with at leastone polar group selected from the group consisting of acid, acid ester,or acid anhydride, or a salt thereof.
 2. The foam of claim 1, whereinthe acid of the acid, acid ester, or acid anhydride, or salt thereof, isa mono-unsaturated carboxylic acid.
 3. The foam of claim 1, wherein theacid is acrylic acid and the acid anhydride is maleic anhydride.
 4. Thefoam of claim 3; wherein the polymer resin graft-modified with at leastone polar group has at least one pendant polar group selected from thegroup consisting of poly(acrylic acid), methyl acetate, succinic acidand maleic anhydride.
 5. The foam of claim 1; wherein the polymer matrixB) comprises at least one polyolefin resin.
 6. The foam of claim 5,wherein the at least one polyolefin resin is at least one ethylenepolymer or at least one propylene polymer, or a mixture of at least oneethylene polymer and at least one propylene polymer, the ethylenepolymer being an ethylene homopolymer or an interpolymer of ethylene andat least one monomer selected from the group consisting of one or moreC₃-C₁₀ α-olefin polymers, and the propylene polymer being a propylenehomopolymer or an interpolymer of propylene with ethylene or one or moreC₃-C₁₀ α-olefin polymers.
 7. The foam of claim 1, wherein theparticulate additive comprises a metal oxide, halide, borate, silicate,or stannate.
 8. The foam of claim 1, wherein the particulate additive isa flame retardant adjuvant selected from the group consisting of a flameretardant synergist, a smoke suppressant or char forming agent, flameretardant, antioxidant, antiblock additive, colorant, pigment, filler,or acid scavenger.
 9. The foam of claim 8, wherein the particulateadditive comprises an antimony oxide flame retardant synergist.
 10. Thefoam of claim 1, wherein the at least one polymer resin of the polymermatrix B) comprises at least one first-category polymer resin that has,on the average, at least one polar group per resin molecule and at leastone second-category polymer resin that has, on the average, less than0.1 polar group per polymer resin molecule.
 11. The foam of claim 10,wherein the at least one second-category polymer resin is an ethylenepolymer or a propylene polymer, or a mixture of an ethylene polymer anda propylene polymer.
 12. The foam of claim 10, wherein the ratio of theaverage melt flow rate of the first-category polymer resin(s) to theaverage melt flow rate of the second-category polymer resin(s), eachmelt flow rate measured according to ASTM D1238 (2.16 kg,.), is in therange from 1:2 to 15:1.
 13. The foam of claim 1 further comprising ahalogenated flame retardant C).
 14. The foam of anyone of claim 10,wherein the first category polymer resin of the polymer matrix B) isgraft modified with at least 0.1 weight-percent polar groups.
 15. Thefoam of claims 10, wherein the first category polymer resin of thepolymer matrix B) is graft-modified with up to 10 weight-percent polargroups.
 16. The foam of claims 10, wherein the weight ratio of the firstcategory polymer resin of the polymer matrix B) to the particulateadditive A) is in the range from 0.1:1 to 3:1.
 17. The foam of claim 1having art average cell size, measured according to ASTM D3575, of atleast 4.5 mm.
 18. The foam of claim 1 having an average sound absorptioncoefficient (measured via ASTM E1050 at 250, 500, 1000 and 2000 hertz(Hz) sound frequencies) of at least 0.15.
 19. The foam of claim 1 in theform of an office partition, automotive decoupler, domestic appliancesound insulation, industrial noise absorber, sound proofing panel,hanging baffle, or machine enclosure.
 20. A Method of Using the foam ofclaim 1 as an acoustic absorption material comprising the step oflocating the foam in the presence of a sound intensity of at least 50decibels.